The royal family announced yesterday that the Duchess of Cambridge, aka Kate Middleton, is expecting her second child—just a little over 13 months after the birth of Prince George. But is it safe to get pregnant again so soon?

When to have your next baby is, of course, a deeply personal decision, and one that isn't always under your control. But research does suggest that having pregnancies too close together—or too far apart—can pose risks to both mom and baby.

Studies have shown that women who wait less than 18 months after giving birth to get pregnant again are more likely to have a premature delivery. Closely spaced pregnancies are also associated with low birthweight and small size for gestational age. Research suggests that having pregnancies less than 12 months apart is associated with an increased risk of complications like placental abruption (when the placenta separates from the wall of the uterus before delivery) and placenta previa (when the placenta partially or completely covers the cervix) in women who delivered their first child via caesarean section. Conceiving within 12 months of giving birth has even been linked to a higher risk of autism in the second child.

Experts think that getting pregnant soon after giving birth may not give a woman's body enough time to recover from the stresses of carrying and delivering a baby. However, it's also possible that the risks are due to behavioral factors that might be more common in women with close-together births, like unplanned pregnancy or skipping prenatal care.

On the flip side, having pregnancies five years or more apart is also linked to preterm birth and low birthweight, as well as preeclampsia (a condition where the mom-to-be develops high blood pressure and excess protein in her urine after 20 weeks of pregnancy).

One thing that's not thought to be linked to pregnancy spacing: the severe, debilitating form of morning sickness known as hyperemesis gravidarum that the Duchess suffered from during her first pregnancy and is unfortunately dealing with again this time around, as Clarence House revealed.

Of course, many other factors besides health risks go into deciding how far apart to space your children, including your own age, your family resources, how many children you eventually want to have, and what kind of relationship you envision your kids having. Fortunately, it's probably safe to assume that Kate is getting the best possible medical care as she gestates the next heir to the throne.